Robin Williams, very open, though, about his struggles throughout his career, no matter how successful he was, he could not shake the demon of addiction. A problem that plagued had imfor decades putting him in and out of rehab and our juju Chang is here with more on that. Good morning, juju. Reporter: It's a tragic truism we all kind of know in our gut that depression and substance abuse also go hand and hand and robin Williams often made self-medicating a punch line to a lot of his jokes but he also knew through years of personal suffering that it was no joking matter. Ah! Reporter: You wouldn't know it from all the hilarious roles he conjured up on screen like Mrs. Doubtfire and "The bi birdcage" but offscreen legendary actor robin Williams was tormented by addiction for decades. A dark demon he frequently joked about on stage. And alcohol is especially dangerous for people like myself alcoholics or you can say ethanol challenged. Whatever you want to call it. Reporter: It wasn't just alcohol, abusing cocaine in the early '80s but quitting after his friend John belushi's overdose telling Barbara Walters about it. He was a one of the toughest people you can meet and it cleaned up a generation of people because he was as strong as anyone you could meet. When we hear about people using drug, most of the time they use it for getting high. For me it was basically a way to escape and cut off from people. Reporter: He told ABC news in 2011 the role of a lifetime that helped keep him sober for 20 years was that of father. The one thing that cleaned me up was having a kid. That's immediate. If that's the same -- I didn't have any rehab or any, you know, any groups. Reporter: But after those two decades of sobriety Williams says he sampled some whiskey in 2006 and within a week he was hooked. His family reportedly staged an intervention. He spoke about the grip of addiction with Diane sawyer just two months after leaving rehab. Away, quiet time, good though and back. People say how do you feel. With my fingers. Just alcohol? Just alcohol. That's enough really. To talk about it as caused by something -- Thought caused by anything. It's just there. Lays in wait for the time when you think I'm fine now, I'm okay and then, beep. And then the next thing you know it's not okay. You're standing at a precipice and you look down, there's a voice and a little quiet choice that says just one. And for someone who has no tolerance for it that's not a possibility. Reporter: Was there something somebody said, one sentence that got through that sailed through -- You're a drunk! No, it's like it got through to me saying you need help and that's the best sentence that got through. Reporter: Williams said he spend years thinking he could handle his alcohol problem on his own. I can do this, I can stop and you really think you can and you realize you can't. Reporter: It was that relapse in 2006 that reportedly cost him his second marriage. Earlier this summer Williams checking into the renown Hazelton clinic to focus on his continued commitment to sobriety. His rep telling ABC news it was not a relapse. The world now left with the advice a wise Williams once gave to a younger version of himself. Don't be running so fast and that's it. How much have you loved? That's a simple question. How much have you loved. Love doing what you do or love being with people. If you can answer that pretty positively you're doing okay. It's a good life. The most profound lesson he is giving us all whenever someone is universally beloved and loses such a hard fought battle with depression it reminds us all this is a brutal, cruel disease that strikes people no matter who you are, how much wealth or stature or support from loved ones somebody has. Robin. All walks of life. You got that right, juju. ABC news senior medical contributor Dr. Jennifer Ashton joins us, addiction, depression. What exactly is that relationship? It's very complicated and we do see quite often they can exist in parallel. I mean, of course, depression can lead to addiction and addiction can lead to depression but they can be two parallel disease processes and when one or both are out of control, they can spiral precipitously downhill very quickly with life-threatening and fatal consequence. We knew so much more about robin Williams' addiction. He talked openly about that but not about the depression. We can talk about cancer and all these different types of diseases and ailments but when it comes to depression, Jen, it seems like there's a stigma attached. Why is that and how do we get past it. We have to get past it. It's something that existed when I was in medical school. It exists today and we keep seeing these well-known figures again and again with their lives lost because in many ways we as a society are not really that equipped to handle embracing something that doesn't have a scar or as you were saying if you're on chemotherapy and lose your hair people can see that. People can't see depression all the time and tears of a clown, right, that famous song, this was what robin Williams embodied and what so many people who live and battle with depression deal with. They can be smiling on the outside and they can be in utter agony and in some cases frankly psychotic on the inside and we need to be more embracing of this and drop the sigma. There are a lot of families shaking their head because they deal with this. It's not just famous people like jooumg said. It's not because you're wealthy. It does not matter. What is the lesson we learn here? Let's not let another person die in vain and increase our awareness and understand when a person is profoundly depressed they need one-to-one help. That's a part of the story this morning. All right. Jen, thanks so much. Appreciate that.

This transcript has been automatically generated and may not be 100% accurate.

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